Chapter 5 of ICD-10-CM — Mental, Behavioral and Neurodevelopmental Disorders, codes F01 through F99 — carries a small set of rules that the CPC exam tests with outsized frequency, because each one overrides an instinct coders bring from other chapters. Substance use codes follow a strict hierarchy where only one code survives. Depression codes hinge on the words “single” and “recurrent.” Dementia codes obey code-first instructions that reverse the expected order. This guide covers the tested territory of the F chapter, building on the conventions in ICD-10-CM Coding Guidelines and the ordering rules in ICD-10 Sequencing Rules.

How Chapter 5 Is Organized

The chapter groups disorders into blocks that the exam expects you to recognize by range: F01–F09 for mental disorders due to known physiological conditions (including the dementias); F10–F19 for substance-related disorders, arranged by substance; F20–F29 for schizophrenia spectrum and other psychotic disorders; F30–F39 for mood disorders, including bipolar disorder and the depressive episodes; F40–F48 for anxiety, obsessive-compulsive, stress-related, and somatoform disorders; F60–F69 for personality disorders; F80–F89 for developmental disorders including autism spectrum disorder; and F90–F98 for disorders with onset in childhood, including ADHD. The chapter pairs constantly with the psychiatry CPT codes covered in Medicine Section CPT Coding, since a psychotherapy or psychiatric evaluation claim needs an F-chapter diagnosis behind it.

The Substance Use Hierarchy: Use, Abuse, Dependence

The F10–F19 blocks give each substance three severity tiers — use, abuse, and dependence — and the guideline the exam tests relentlessly: when the documentation describes more than one tier for the same substance, assign only one code, following the hierarchy. If both use and abuse are documented, code abuse. If abuse and dependence are documented, code dependence. If use, abuse, and dependence all appear, code only dependence. One substance, one code, highest tier wins.

The structure within each block is consistent: the fourth character sets the tier (for alcohol, F10.1- abuse, F10.2- dependence, F10.9- use), and later characters capture complications — intoxication, withdrawal, induced mood or psychotic disorders. Two supporting rules complete the picture. “In remission” codes (such as alcohol dependence in remission, F10.21) require the provider’s documentation of remission — a coder never infers it. And the unspecified “use” codes are assigned only when the substance use is documented as associated with a mental or behavioral disorder or medical condition — social drinking mentioned in passing is not coded at all. Blood alcohol level, when documented, takes an additional Y90 code.

Nicotine: The Substance the Exam Sneaks In

Tobacco is the most commonly documented substance in the F10–F19 block, and the exam favors it because nicotine’s codes scatter across three chapters. Nicotine dependence lives at F17.2-, with the fifth character naming the product — F17.21- for cigarettes, with parallel characters for chewing tobacco and other products — and the final character capturing complications: F17.210 is nicotine dependence, cigarettes, uncomplicated, while F17.211 is the same dependence in remission, which, like every remission code in this chapter, requires the provider’s explicit documentation. Two Z-chapter neighbors complete the set and supply the distractors. Tobacco use without documented dependence is Z72.0 — a lifestyle code, not an F code — and a former smoker’s history of nicotine dependence is Z87.891, one of the most frequently assigned codes in all of ICD-10-CM because it rides along on so many encounters as a risk factor. The selection logic mirrors the tier hierarchy: dependence documented, code F17.2-; current use without dependence, Z72.0; quit and documented as such, Z87.891 — and never more than one of the three for the same patient on the same claim. Pregnancy adds a sequencing twist: smoking that complicates pregnancy takes an O99.33- code first, with the F17 code secondary, following Chapter 15’s sequencing priority as covered in ICD-10 Pregnancy Coding and O Codes.

Depression: Single vs Recurrent, and Severity

Major depressive disorder splits into two categories on one word: F32 for a single episode, F33 for recurrent episodes — and the exam plants “recurrent” quietly in the history. Within each, the fourth character grades severity: mild, moderate, severe without psychotic features, severe with psychotic features, plus characters for partial and full remission. So moderate recurrent major depression is F33.1, while a single severe episode with psychotic features is F32.3. Unspecified depression, F32.A or F32.9 territory, exists for thin documentation — but when the record grades severity and episode course, the specific code is required, per the highest-specificity principle in ICD-10-CM Coding Guidelines.

Bipolar Disorder Absorbs the Depression

Bipolar disorder (F31) carries its own hierarchy rule: once bipolar disorder is documented, depressive episodes are coded within F31 — bipolar disorder, current episode depressed — never with the F32/F33 major depression codes. The F31 fourth and fifth characters identify the current episode type (hypomanic, manic, depressed, mixed) and severity. A vignette documenting “bipolar disorder, current episode depressed, severe” that offers an F33 answer choice is testing exactly this absorption rule.

Anxiety, Stress, and Somatoform Disorders

The F40–F48 block supplies steady exam vocabulary. Generalized anxiety disorder is F41.1; panic disorder without agoraphobia is F41.0; the phobic disorders sit in F40 with agoraphobia distinguished by panic-disorder status. Post-traumatic stress disorder codes to F43.1- with characters for acute versus chronic, and adjustment disorders (F43.2-) subdivide by presentation — with depressed mood, with anxiety, mixed. The somatoform territory holds a distinction worth knowing: psychological-factor pain codes to F45.41 (pain disorder exclusively related to psychological factors), while F45.42 (pain disorder with related psychological factors) is used with a G89 code identifying the pain itself — a combination-code interaction in the spirit of Combination Codes in ICD-10.

Dementia and the Code-First Rules

The F01–F09 block reverses the sequencing instinct. Vascular dementia (F01.-) classifies dementia due to cerebrovascular disease, with the etiology relationship built into the category itself. The heavily tested pattern is F02 — dementia in other diseases classified elsewhere — which is a manifestation category: the underlying disease is coded first (Alzheimer’s disease G30.-, Parkinson’s disease G20, Huntington’s disease G10), followed by the F02 code, with characters capturing severity and the presence of behavioral disturbances such as agitation or wandering. Unspecified dementia without a documented cause is F03.9-. The exam’s favorite construction: “Alzheimer’s dementia with behavioral disturbance” — G30.9 first, then the F02.8- code with the behavioral character, and any answer leading with the F code is wrong on sequencing alone. These etiology/manifestation pairs follow the convention machinery covered in Excludes1 and Excludes2 Notes and the chapter conventions of the guidelines.

Schizophrenia, ADHD, and Autism

Three more testable families round out the chapter. Schizophrenia (F20.-) divides by type with paranoid schizophrenia (F20.0) the most cited, and schizoaffective disorder (F25.-) as its neighbor-trap. Attention-deficit hyperactivity disorder (F90.-) splits by presentation: predominantly inattentive (F90.0), predominantly hyperactive (F90.1), combined (F90.2). Autism spectrum disorder is F84.0. These are one-fact vocabulary questions — the exam gives the disorder name and expects the category — with the clinical language grounded in Medical Terminology for Coders.

High-Yield F Codes Reference Table

The chapter’s most tested codes fit in one table — the exam draws its vocabulary questions almost entirely from this set:

F Codes and Medical Necessity

Because behavioral health claims pair F codes with time-based psychotherapy CPT codes, the diagnosis does double duty: it identifies the condition and it supports medical necessity for the service billed. Payers routinely require a covered F-chapter diagnosis for psychotherapy codes, and an unspecified code where the record supports specificity is a denial risk — the same necessity logic covered from the payer side in the Compliance & Regulatory Guide for the CPC Exam. For coders, the operational rule is unchanged: code what the provider documents, to the highest specificity documented, and query rather than infer.

Worked Example: One Chart, Three Rules

Documentation reads: “Patient with alcohol abuse and alcohol dependence, currently in a severe recurrent major depressive episode; history also notes Alzheimer’s dementia in the patient’s mother.” Apply the rules in order. Substance hierarchy: abuse and dependence both documented for alcohol — code only dependence (F10.20, uncomplicated, absent documented complications). Depression: recurrent plus severe without psychotic mention — F33.2. Family history: the mother’s Alzheimer’s is not the patient’s condition; it becomes a Z-family history code if relevant, never a G30/F02 pair, connecting to the status-code discipline in Z Codes in ICD-10. Three sentences, three rules, three codes — and every distractor pattern (F10.10 for abuse, F32.2 for single episode, a dementia code for the mother) violates exactly one.

How the CPC Exam Tests Chapter 5

Pattern 1 — The Hierarchy Collapse

Use, abuse, and dependence documented in any combination for one substance. One code survives: the highest tier.

Pattern 2 — Single vs Recurrent

A depression vignette hides “second episode” or “recurrence” in the history, moving the answer from F32 to F33 — with severity finishing the character.

Pattern 3 — Dementia Sequencing

Alzheimer’s or Parkinson’s dementia with or without behavioral disturbance: underlying disease code first, F02 manifestation code second, behavioral character last.

Pattern 4 — Bipolar Absorption

A depressive episode in a documented bipolar patient codes to F31’s current-episode-depressed codes, never to F32/F33.

Common Mistakes

Coding both abuse and dependence for the same substance. The hierarchy permits only one code per substance — dependence over abuse, abuse over use.

Assigning “in remission” without provider documentation. Remission codes require the provider’s explicit statement; a coder cannot infer remission from clean toxicology or elapsed time.

Missing the word “recurrent.” F32 versus F33 turns entirely on episode history, and the severity characters then mirror each other.

Using F32/F33 for a bipolar patient’s depression. Documented bipolar disorder absorbs depressive episodes into F31’s current-episode codes.

Sequencing the F02 dementia code before the underlying disease. F02 is a manifestation code: Alzheimer’s (G30.-), Parkinson’s (G20), or the other physiological cause codes first.

Coding social or casual substance use. The use-tier codes apply only when the use is linked to a documented disorder or condition; incidental mention is not coded.

Coding family psychiatric history as the patient’s diagnosis. A relative’s condition takes a family-history Z code when relevant, never the disorder’s F code on the patient’s claim.

Final Exam Strategy for This Section

Chapter 5 is four rules and a vocabulary list: the substance hierarchy, single-versus-recurrent, bipolar absorption, and dementia’s code-first sequencing — plus category recognition for GAD, PTSD, schizophrenia, ADHD, and autism. Write the four rules on one line each beside your CPC Exam Cheat Sheet tables, run the worked-example chart above until each rule fires automatically, and recycle misses through the CPC Exam Study Guide drill loop. The chapter’s questions are short, the rules are absolute, and the points are among the most reliable on the exam.

Frequently Asked Questions

Every drug-related diagnosis question on the CPC exam turns on a single classification decision made before any code is touched: was this a poisoning, an adverse effect, or underdosing? The three categories share the same T36–T50 code range and the same Table of Drugs and Chemicals, but they carry different final characters, opposite sequencing rules, and different supporting codes — so the classification decision determines everything downstream. This guide defines the three categories, walks through the Table of Drugs column by column, and drills the sequencing rules that the exam tests more reliably than almost any other ICD-10 guideline, building on the lookup discipline from The ICD-10 Alphabetic Index and the ordering principles in ICD-10 Sequencing Rules.

The Three Categories Defined

A poisoning is any improper use of a medication or exposure to a harmful substance: an overdose, the wrong drug taken or administered in error, a drug taken by the wrong route, a prescribed drug taken with alcohol, or a prescription medication combined with an over-the-counter drug the prescriber didn’t sanction. The defining feature is that something went wrong in the taking — the harm did not arise from a correctly prescribed, correctly administered drug.

An adverse effect is the opposite setup: the drug was correctly prescribed and properly administered, and the patient still suffered a harmful reaction — an allergic response, digoxin toxicity at a therapeutic dose, tachycardia from an appropriately taken bronchodilator. Nothing was done wrong; the body simply reacted badly.

Underdosing means the patient took less of a medication than prescribed, or discontinued it, whether deliberately (cost, side effects, personal choice) or inadvertently (forgetting doses). The clinical consequence is usually the return or worsening of the condition the drug was meant to control, and the coding is built around capturing exactly that.

Navigating the Table of Drugs and Chemicals

The Table of Drugs and Chemicals is an alphabetical index of substances, and each substance row spans six columns: four poisoning intents — accidental (unintentional), intentional self-harm, assault, and undetermined — plus adverse effect and underdosing. Classifying the scenario picks the column; the substance picks the row; the intersection supplies the code, which is then verified in the Tabular List like any index entry, per the method in The ICD-10 Alphabetic Index.

Two default rules govern the intent columns and appear constantly in exam distractors. If the intent of a poisoning is not documented, code it as accidental — the accidental column is the default. The undetermined column is reserved for cases where the provider has affirmatively documented that intent cannot be established; silence about intent is not “undetermined.”

How the T36–T50 Codes Are Built

The drug toxicity codes are combination codes of the kind described in Combination Codes in ICD-10: a single code carries the substance, the category (poisoning by intent, adverse effect, or underdosing), and — with its 7th character — the episode of care. The fifth or sixth character encodes the classification: characters 1 through 4 correspond to the four poisoning intents, character 5 marks an adverse effect, and character 6 marks underdosing. Many codes need the placeholder X to keep the 7th character in position, following the mechanics in Injury Coding and 7th Characters. So T39.011A is poisoning by aspirin, accidental, initial encounter; T46.0X5A is adverse effect of digoxin (a cardiac glycoside), initial encounter; T45.526D is underdosing of antithrombotic drugs, subsequent encounter. Because the intent lives inside the code, no separate external cause code is needed for the poisoning itself — the T code does that work alone.

Sequencing: The Rule That Flips

The exam’s favorite drug question is pure sequencing, because the order reverses between categories. For a poisoning, the T code is sequenced first, followed by codes for the manifestations — the respiratory depression, the altered mental status, the gastrointestinal bleed. Poisoning leads; effects follow.

For an adverse effect, the order flips: code first the nature of the adverse effect — the bradycardia, the rash, the acute kidney injury — followed by the T code with fifth or sixth character 5 identifying the responsible drug. Manifestation leads; drug code follows.

For underdosing, the underdosing T code is never permitted as a principal or first-listed diagnosis. The relapse or exacerbation of the underlying condition is coded first — the recurrent seizures, the uncontrolled hypertension — followed by the underdosing code, plus a code explaining why the patient underdosed: noncompliance codes from Z91.12- (intentional, including the financial-hardship code) or Z91.13- (unintentional), or a complication-of-care code when a device or caregiver issue is responsible. Those status and noncompliance codes come from the family covered in Z Codes in ICD-10.

A memory device that survives exam pressure: Poisoning leads, Adverse effect follows, Underdosing never leads.

Toxic Effects of Non-Medicinal Substances (T51–T65)

Substances that are harmful by nature — alcohol, carbon monoxide, lead, solvents, pesticides, venom — are classified to categories T51–T65 as toxic effects rather than poisonings. These codes share the intent structure (accidental, self-harm, assault, undetermined) and the same 7th-character conventions, and the same default-to-accidental rule applies. Toxic effect codes are sequenced first, ahead of the manifestations, exactly like poisonings — and this is the family that leads corrosion coding, as covered in Burn Coding in ICD-10. A carbon monoxide exposure with headache and confusion leads with the T58 code for the CO source, followed by the symptom codes per the guidance in Coding Signs and Symptoms in ICD-10.

7th Characters and Episodes of Care

All codes in T36–T65 require a 7th character: A for the initial encounter while the patient is receiving active treatment, D for subsequent encounters during recovery, and S for sequela — the late effects, such as anoxic brain damage persisting after a poisoning has resolved. The sequela pattern pairs the residual condition code with the T code carrying 7th character S, mirroring the burn-scar construction and the general rules in Injury Coding and 7th Characters. Watch the placeholder X: a five-character code like T46.0X5 needs the X to push the classification character into position five and the encounter character into position seven.

Worked Example: Three Scenarios, One Drug

Warfarin makes the classification decision vivid because all three categories are clinically common. Scenario one: a patient mistakenly takes double his prescribed warfarin dose and develops a GI bleed — a poisoning, accidental; the T45.51 poisoning code with intent character and 7th character A leads, followed by the GI hemorrhage code. Scenario two: a patient taking warfarin exactly as prescribed develops bleeding from a drug interaction his providers sanctioned — an adverse effect; the hemorrhage codes lead, followed by T45.515A as the adverse-effect identifier. Scenario three: a patient stops filling her warfarin because of cost and suffers a thrombotic stroke — underdosing; the stroke codes lead, then the underdosing code T45.516A, then Z91.120 for intentional noncompliance due to financial hardship. Same drug, three sequencing patterns — and the exam can build a question from any of them.

How the CPC Exam Tests This Material

Pattern 1 — Classify, Then Sequence

The vignette describes how the drug was taken and what happened. Classify first: improper use is poisoning, proper use is adverse effect, less-than-prescribed is underdosing. Then apply the matching sequence — poisoning first, manifestation first, or condition-then-underdosing.

Pattern 2 — The Intent Default

A poisoning scenario is silent about intent, and the choices split between accidental and undetermined codes. Undocumented intent defaults to accidental; undetermined requires explicit documentation that intent cannot be established.

Pattern 3 — Alcohol and OTC Interactions

A prescribed drug taken with alcohol, or mixed with an unsanctioned over-the-counter medication, reads like an adverse effect but is classified as a poisoning — the taking was improper even though the prescription was valid.

Pattern 4 — Underdosing Consequences

A patient reduced or stopped a medication and the underlying disease returned. The exacerbated condition is first-listed, the underdosing T code follows, and a Z91.12-/Z91.13- code explains the noncompliance — any answer leading with the underdosing code is wrong on its face.

Common Mistakes

Coding a drug-with-alcohol interaction as an adverse effect. Any interaction with alcohol, or with a non-sanctioned over-the-counter drug, makes the event a poisoning regardless of a valid prescription.

Sequencing the manifestation first in a poisoning. Poisoning codes lead; the respiratory depression, bleeding, or altered mental status follows.

Sequencing the drug code first in an adverse effect. The nature of the adverse effect is coded first, with the T code (character 5) following to identify the drug.

Listing an underdosing code as the first-listed diagnosis. Underdosing codes are never principal or first-listed; the relapsed condition leads, with noncompliance codes added to explain why.

Choosing the undetermined intent column by default. Undetermined requires documentation that intent cannot be established; otherwise undocumented intent codes as accidental.

Adding a separate external cause code for the poisoning. The T36–T50 combination codes carry substance and intent internally; no additional external cause code is assigned for the poisoning event.

Dropping the placeholder X or the 7th character. Codes like T46.0X5A need the X to keep the classification and encounter characters in their correct positions.

Final Exam Strategy for This Section

Every question in this family is a two-step problem wearing a long vignette: classify the event, then apply that category’s sequencing rule. Write the three-line summary — poisoning leads, adverse effect follows, underdosing never leads — into your review notes beside the intent-default rule, and drill the warfarin triple until the classification is instant. Add the Table of Drugs columns to your CPC Exam Cheat Sheet review page, and work missed scenarios through the loop in the CPC Exam Study Guide. Alongside the framework in ICD-10-CM Coding Guidelines, this is among the highest-return topics you can master in a single study session — the rules are few, absolute, and tested on virtually every exam form.

Frequently Asked Questions

Burn coding is one of the few places on the CPC exam where you may need to do arithmetic before you can pick a code. A burn scenario asks for three separate decisions — the site-and-degree codes, the sequencing order when multiple burns exist, and the T31 extent code built from total body surface area percentages — and the exam routinely folds all three into a single question. The good news is that the system is completely mechanical once you know the rules. This guide covers burn degrees, the Rule of Nines calculation, the two-axis T31 codes, corrosions, the 7th-character requirements, and the CPT codes for burn treatment, building on the injury-coding framework in Injury Coding and 7th Characters and the ordering rules in ICD-10 Sequencing Rules.

Burn Degrees and How ICD-10 Classifies Them

ICD-10-CM classifies burn severity in three degrees, and the vignette’s clinical language maps directly onto them. First-degree burns involve erythema — redness of the epidermis only, like a typical sunburn reaction. Second-degree burns involve blistering and damage into the dermis; documentation may say “partial thickness.” Third-degree burns involve full-thickness destruction of the skin, documented as “full thickness” or with references to eschar or charring. The burn categories are organized by anatomical site: T20 for the head, face, and neck; T21 for the trunk; T22 for the shoulder and upper limb except the wrist and hand; T23 for the wrist and hand; T24 for the lower limb except the ankle and foot; T25 for the ankle and foot. Three special categories complete the set — T26 for burns confined to the eye and adnexa, T27 for the respiratory tract, and T28 for other internal organs — and these internal burn categories classify by site only, not by degree.

Within each site category, the code characters specify the degree and the precise location, and each distinct burn site receives its own code. When one site has burns of more than one degree — a forearm with second- and third-degree areas — only the highest degree for that site is coded. One boundary note the exam likes: an ordinary sunburn is not a T-section burn at all; it codes to L55 in the skin chapter. The T burn categories cover thermal burns from heat sources, electricity, and radiation, while chemical burns take the parallel corrosion codes described below.

The Rule of Nines: Calculating TBSA

The Rule of Nines divides the adult body into regions of nine percent — or multiples of nine — so total body surface area (TBSA) burned can be estimated quickly.

The percentages sum to 100 across the whole body. Infants and small children carry proportionally larger heads and smaller legs, so pediatric assessments adjust the percentages, and providers may document TBSA directly from a Lund-Browder chart — in which case you use the documented percentage rather than recalculating. On the exam, the arithmetic is deliberately simple: an adult with burns covering one entire arm and the anterior trunk has 9 + 18 = 27 percent TBSA. Do the addition on scratch paper before looking at any answer choice, because the distractors are built from the most common addition mistakes.

T31 and T32: The Two-Axis Extent Codes

Category T31 (burns) and T32 (corrosions) classify burns by extent, and each code carries two axes. The fourth character reports the total TBSA burned, in ten-percent deciles: T31.0 for less than 10 percent, T31.1 for 10–19 percent, up to T31.9 for 90 percent or more. The fifth character reports how much of that total is third-degree, in the same deciles: 0 for less than 10 percent third-degree (or none), 1 for 10–19 percent, and so on. The fifth character can never represent a larger percentage than the fourth, since the third-degree portion is a subset of the total.

Read T31.42 with that grammar: total burns covering 40–49 percent of the body, of which 20–29 percent is third-degree. The exam tests this decoding in both directions — building the code from stated percentages and translating a code back into percentages. The guidelines assign T31 a supporting role: use it as an additional code alongside the site-specific burn codes when reporting data on burn mortality or when the extent is needed (many payers and registries require it for third-degree burns), and use it alone only when the burn sites are not documented.

Sequencing Multiple Burns

When a patient has multiple burns, the ICD-10-CM guideline is direct: sequence first the code reflecting the burn of the highest degree. A patient with a third-degree burn of the hand and a second-degree burn of the chest lists the T23 third-degree code first, then the T21 second-degree code, then the T31 extent code as an additional code. When the encounter is for something other than the burns — treatment of related inhalation injury, for example — the usual reason-for-encounter logic from Principal vs First-Listed Diagnosis still governs, but among the burn codes themselves, highest degree always leads.

Burns vs Corrosions

Every burn category has a corrosion twin: corrosions are injuries from chemicals — acids, alkalis, caustics — while burns are thermal, from heat, flame, electricity, or radiation. The corrosion codes occupy the same site categories with parallel structure, and T32 mirrors T31 for extent. The coding mechanics are identical, with one addition: for corrosions, a code from categories T51–T65 identifying the chemical substance and intent is sequenced first, followed by the corrosion site codes. The exam signal is pure vocabulary — “splashed with drain cleaner” is a corrosion, “scalded by boiling water” is a burn — and choosing the wrong family is the intended trap.

7th Characters and Episode of Care

Burn codes in T20–T28 require the standard injury 7th characters: A for the initial encounter (active treatment), D for subsequent encounters during routine healing, and S for sequela. Two applications are burn-specific and testable. First, a burn that fails to heal — a non-healing burn or infected burn site — is still coded as an acute burn with the active-treatment logic, because the condition remains under active management. Second, sequelae of burns are common and long-lived: scars and contractures appearing after healing are coded with the scar or contracture code plus the burn code with 7th character S to identify the cause. The placeholder-X mechanics and encounter definitions follow the rules detailed in Injury Coding and 7th Characters, and external cause codes for the source, intent, and place of the burn round out the picture per ICD-10-CM Coding Guidelines.

Burn Treatment CPT Codes

The procedural side of burn care has its own compact code family. Initial treatment of a first-degree burn, when no more than local treatment is required, is 16000. Dressings and/or debridement of partial-thickness burns are coded by the size of the treated surface: 16020 for small (less than 5 percent TBSA), 16025 for medium (5 to 10 percent), and 16030 for large (greater than 10 percent). Escharotomy — incision through constricting burned tissue to restore circulation — is 16035 for the initial incision and add-on 16036 for each additional incision. Extensive debridement and excision of burn wounds beyond dressings connect to the wound-management codes covered in Wound Repair Coding, and definitive coverage of full-thickness losses moves into grafting, covered in the Skin Graft Coding CPT Guide. Note that the TBSA percentages driving CPT code selection are the same percentages you calculated for T31 — one Rule of Nines computation serves both code sets.

Worked Example: A Complete Burn Encounter

An adult presents for initial treatment after a kitchen fire: third-degree burns across the anterior trunk and second-degree burns of the entire right arm. Start with TBSA: anterior trunk 18 percent plus one arm 9 percent equals 27 percent total, of which 18 percent is third-degree. Build the diagnosis list: the T21 third-degree anterior trunk burn code with 7th character A leads (highest degree first), the T22 second-degree arm code with A follows, then T31.21 — total TBSA in the 20–29 band (fourth character 2), third-degree portion in the 10–19 band (fifth character 1) — plus external cause codes for the flame exposure and place of occurrence. If the physician performed dressings and debridement of the partial-thickness component over roughly 9 percent TBSA, the CPT service is 16025, medium. Every burn question on the exam is a subset of this walkthrough.

How the CPC Exam Tests Burn Coding

Pattern 1 — Build the T31 Code from Percentages

The vignette states or implies TBSA percentages and asks for the extent code. Add the Rule of Nines regions, assign the fourth character from total TBSA and the fifth from the third-degree portion, and reject any answer whose fifth character exceeds its fourth.

Pattern 2 — Sequencing Multiple Burn Sites

Two or more burns of different degrees at different sites. The highest-degree burn is sequenced first, each site gets its own code, and same-site burns of multiple degrees collapse to the highest degree only.

Pattern 3 — Burn or Corrosion?

The scenario names the agent. Heat, flame, electricity, and radiation are burns; acids, alkalis, and chemicals are corrosions with a T51–T65 chemical code sequenced ahead of them.

Pattern 4 — Matching the CPT Burn Treatment Code

A dressing-and-debridement scenario supplies a TBSA percentage. Map it to 16020, 16025, or 16030 by the small/medium/large thresholds, reserving 16000 for first-degree-only treatment and 16035–16036 for escharotomy.

Common Mistakes

Letting the fifth character of T31 exceed the fourth. The third-degree percentage is a subset of total TBSA; a code like T31.24 is impossible and will appear among distractors.

Coding every degree present at a single site. When one site has second- and third-degree burns, only the highest degree for that site is coded.

Sequencing burns by narrative order instead of degree. The highest-degree burn leads regardless of the order the vignette mentions the injuries.

Coding sunburn with T-section burn codes. Sunburn classifies to L55 in the skin chapter, not to the burn categories.

Treating chemical injuries as thermal burns. Chemical agents produce corrosions with parallel codes and a required T51–T65 code identifying the chemical.

Forgetting T31 when the payer or registry needs extent. The site codes alone do not capture TBSA; T31/T32 is the vehicle for extent and is required reporting for many third-degree burns.

Dropping the 7th character or misusing S. Active treatment takes A, routine healing follow-up takes D, and scars or contractures after healing take the residual-condition code plus the burn code with S.

Final Exam Strategy for This Section

Burn questions reward a fixed sequence: calculate TBSA with the Rule of Nines, identify each site and its highest degree, order the site codes by degree, build the T31 code from your two percentages, and only then look at the answer choices. The entire topic fits on one review card — the six site categories, the nine-percent regions, the T31 two-axis grammar, and the 16000-series treatment thresholds — so add that card to your CPC Exam Cheat Sheet materials and drill a handful of percentage scenarios using the method in the CPC Exam Study Guide. Arithmetic under time pressure is only intimidating until it becomes routine.

Frequently Asked Questions

Chapter 15 of ICD-10-CM — Pregnancy, Childbirth and the Puerperium, codes O00 through O9A — comes with its own sequencing priority, its own time axis in the form of trimesters and weeks of gestation, and its own supporting cast of Z codes for delivery outcomes and newborn status. The CPC exam reliably includes pregnancy questions because the chapter’s rules override the general conventions candidates have practiced everywhere else. This guide works through the chapter’s structure, the trimester and Z3A mechanics, the strict criteria for normal delivery code O80, the major complication families, and the fetus-identification 7th characters, building on the sequencing foundation in ICD-10 Sequencing Rules and the chapter conventions covered in ICD-10-CM Coding Guidelines.

Chapter 15 Structure and the Priority Rule

The chapter’s first rule is jurisdictional: O codes belong on the maternal record only, never on the newborn’s record. The newborn gets its own codes from Chapter 16 and the Z38 series discussed below. The second rule is the one the exam tests hardest: Chapter 15 codes take sequencing priority over codes from other chapters. When a pregnant patient is treated for any condition affecting the pregnancy, the appropriate O code is sequenced first, with codes from other chapters following to add specificity. A pregnant patient treated for a urinary tract infection is not coded first to the Chapter 14 infection code — the encounter leads with the O code for genitourinary infection in pregnancy, followed by the code identifying the specific organism or condition.

The only escape from this priority is the physician’s explicit documentation that the pregnancy is incidental to the encounter — the condition being treated has nothing to do with, and is not affected by, the pregnancy. In that case, Z33.1 (pregnant state, incidental) is reported as a secondary code and the pregnancy chapter is bypassed entirely. The choice between leading with an O code and adding Z33.1 is the provider’s call, documented, not the coder’s assumption — a principle consistent with the documentation rules threaded through Principal vs First-Listed Diagnosis.

Routine supervision of a normal pregnancy with no complications uses the Z34 series (encounter for supervision of normal pregnancy), while supervision of a high-risk pregnancy — such as one with a history of infertility or prior pregnancy loss — uses category O09, a Chapter 15 category despite being supervisory. Both are first-listed codes for those routine encounters and are not combined with each other.

Trimester Assignment

Most Chapter 15 codes carry the trimester in their final character, and ICD-10-CM defines the boundaries precisely: the first trimester runs from the start of pregnancy to less than 14 weeks 0 days; the second from 14 weeks 0 days to less than 28 weeks 0 days; and the third from 28 weeks 0 days until delivery. Trimester assignment is based on the trimester at the date of the encounter, not the trimester in which a complication first arose — with the standard inpatient exception that if the condition developed during the admission, the trimester at admission governs. Not every code offers every trimester option, because some conditions can only occur in certain windows, and codes exist for “unspecified trimester” that should be reserved for genuinely undocumented cases rather than used as a shortcut. The character-by-character logic of these codes follows the anatomy described in ICD-10 Code Structure.

Z3A: Weeks of Gestation

Category Z3A reports the specific weeks of gestation — Z3A.32 for 32 weeks, for example — and it is an additional code, never first-listed. The guideline instructs coders to assign a Z3A code alongside Chapter 15 codes to identify the specific week of the pregnancy, when known. The exceptions are just as testable as the rule: Z3A codes are not assigned for abortive outcome encounters (categories O00–O08), for elective termination (Z33.2), or for postpartum conditions, since the pregnancy has ended and weeks of gestation no longer apply.

Normal Delivery: The Strict Criteria of O80

Code O80 — encounter for full-term uncomplicated delivery — is the most exacting code in the chapter, and the exam tests its boundaries. O80 requires a full-term, normal, spontaneous vaginal delivery of a single, healthy infant, with no complications antepartum, during delivery, or postpartum during the admission. Any complication anywhere in that window disqualifies O80, as does any delivery requiring instrumentation or cesarean. When O80 applies, it is always the principal or first-listed diagnosis, it is never accompanied by any other Chapter 15 code, and its only permissible delivery outcome code is Z37.0, single live birth. A vignette that mentions a first-degree laceration, a preterm delivery at 36 weeks, or twins has already excluded O80 — the presence of any of those details in an O80 answer choice is the trap itself.

Outcome of Delivery (Z37) and Liveborn Infant (Z38)

Every maternal delivery record carries exactly one code from category Z37, outcome of delivery: Z37.0 for a single live birth, Z37.1 for a single stillbirth, Z37.2 for twins both liveborn, and so on through the multiple-birth combinations. Z37 is always a secondary code on the maternal record for the delivery encounter only — it does not repeat on postpartum visits.

Category Z38 is Z37’s mirror image on the other chart: it reports the liveborn infant on the newborn’s record, assigned once, at birth, as the principal diagnosis of the birth admission, classified by place of birth and delivery method — Z38.00 for a single liveborn delivered vaginally in hospital, Z38.01 for a single liveborn delivered by cesarean. The pairing rule that resolves every exam question: Z37 on the mother’s record, Z38 on the baby’s, never the reverse, and never both on one chart. The broader status-code logic behind these categories is covered in Z Codes in ICD-10.

Complications: Diabetes, Hypertension, and Infection

The complication categories supply the chapter’s combination-code workload, following the patterns explained in Combination Codes in ICD-10. Diabetes splits along a pre-existing versus gestational axis: pre-existing type 1 or type 2 diabetes complicating pregnancy is coded to O24.0- or O24.1- respectively, followed by the appropriate diabetes code from Chapter 4 as instructed, applying the diabetes logic from Diabetes Coding in ICD-10. Gestational diabetes — arising during pregnancy — codes to subcategory O24.4-, with final characters distinguishing diet-controlled from insulin-controlled disease; when both diet and insulin control are documented, the insulin-controlled code takes precedence. A patient whose gestational diabetes is controlled by diet alone in the second trimester is O24.410 — and no Chapter 4 code accompanies gestational diabetes.

Hypertension follows the same pre-existing versus arising-in-pregnancy split: pre-existing hypertension complicating pregnancy sits in category O10, gestational hypertension without significant proteinuria in O13, and pre-eclampsia in O14, graded mild to severe with HELLP syndrome at O14.2-. Eclampsia — pre-eclampsia with seizures — occupies O15. The progression logic parallels the staged thinking in Hypertension Coding in ICD-10. Infections of the genitourinary tract in pregnancy code to category O23, sequenced ahead of the organism code, and sepsis in pregnancy has its own O85/O86 territory postpartum, connecting to the severity framework in Sepsis Coding ICD-10 Guidelines.

Fetus Identification: 7th Characters in Multiple Gestations

Certain Chapter 15 categories — including O31 (complications specific to multiple gestation), O32 (maternal care for malpresentation), O33.3–O33.6 ranges, O35, O36, O40, O41, O60.1, O60.2, O64, and O69 — require a 7th character identifying which fetus the complication affects. Seventh character 1 through 9 identifies fetus 1 through fetus 9, and 7th character 0 is used for singleton pregnancies or when the affected fetus cannot be determined. The mechanics work exactly like the 7th characters covered in Injury Coding and 7th Characters, including the placeholder-X requirement when the code has fewer than six characters before the 7th. A twin pregnancy with malpresentation of the second twin takes the O32 code with 7th character 2; the same complication in a singleton takes 7th character 0.

Abortive Outcomes: O00–O08

The chapter opens with pregnancies that end early, and these categories carry their own rule set. Ectopic pregnancy (O00) is coded by site — tubal, ovarian, abdominal — with characters distinguishing whether an intrauterine pregnancy coexists. Spontaneous abortion coding turns on completeness: a complete spontaneous abortion in a single encounter codes to O03.9, while incomplete abortion, with retained products of conception, takes codes from the incomplete range and drives different procedural work on the CPT side. Missed abortion — fetal death before 20 weeks with retained products and no symptoms — is O02.1. Complications following these events (infection, hemorrhage, embolism) are captured within categories O03–O07 through their character structure or with O08 codes when complications follow ectopic and molar pregnancies. Two boundary rules matter for the exam: the Z3A weeks-of-gestation codes are never assigned with the O00–O08 categories, and a threatened abortion where the pregnancy continues is coded to O20.0 (hemorrhage in early pregnancy) rather than anything in the abortive range — the pregnancy is still ongoing, so the ordinary Chapter 15 machinery applies.

The Postpartum and Peripartum Periods

The puerperium — the postpartum period — runs for six weeks after delivery, and the peripartum period is defined as the last month of pregnancy through five months following delivery. A postpartum complication is coded with the appropriate Chapter 15 code whenever it occurs within the six-week window, and the guidelines permit Chapter 15 codes even after that window when the provider documents that a condition is pregnancy-related. Routine postpartum follow-up with no complications uses Z39.2 (encounter for routine postpartum follow-up), while complications like postpartum hemorrhage (O72) or puerperal sepsis (O85) stay in the O chapter. Peripartum cardiomyopathy (O90.3) is the classic exam example of a condition defined by the peripartum window itself.

Worked Example: A Complicated Delivery Encounter

A patient at 37 weeks with insulin-controlled gestational diabetes delivers a single liveborn vaginally; delivery is complicated by a second-degree perineal laceration. Build the maternal record from the rules: the delivery complication and conditions are Chapter 15 codes — the perineal laceration codes to O70.1 (second-degree perineal laceration during delivery), and the gestational diabetes shifts from its “in pregnancy” code to the childbirth version because this is the delivery encounter: O24.424 (gestational diabetes mellitus in childbirth, insulin-controlled). Add Z3A.37 for the weeks of gestation and Z37.0 for the single live birth outcome. O80 is impossible twice over — the laceration and the diabetes each disqualify it. The newborn’s chart, built separately, leads with Z38.00. Every element of the exam’s pregnancy questions is in that walkthrough: chapter priority, the childbirth-versus-pregnancy final characters, Z3A, Z37/Z38 jurisdiction, and the O80 exclusion.

How the CPC Exam Tests Chapter 15

Pattern 1 — Sequencing Priority vs Incidental Pregnancy

A pregnant patient is treated for a seemingly unrelated condition. Unless the provider documented the pregnancy as incidental (supporting Z33.1 as secondary), the Chapter 15 code leads and the other-chapter code follows.

Pattern 2 — The O80 Disqualifier Hunt

A delivery vignette buries one small complication — a laceration, an instrument assist, a preterm gestational age. Any one detail disqualifies O80 and forces specific complication codes with the correct Z37 outcome.

Pattern 3 — Trimester and Z3A Assignment

The vignette gives weeks of gestation and asks for complete coding. Convert weeks to the correct trimester character using the 14/28-week boundaries and append the matching Z3A code — remembering Z3A never applies to abortive outcomes or postpartum encounters.

Pattern 4 — Which Chart Gets Which Code

A delivery question mixes maternal and newborn details. O codes and Z37 belong to the mother; Z38 and Chapter 16 codes belong to the newborn — any answer crossing that line is wrong regardless of its other merits.

Common Mistakes

Assigning O codes to the newborn record. Chapter 15 codes describe the mother; the newborn’s birth admission leads with Z38 and uses Chapter 16 for perinatal conditions.

Sequencing a non-pregnancy code first for a pregnant patient. Chapter 15 has sequencing priority unless the provider explicitly documents the pregnancy as incidental, in which case Z33.1 is added as secondary.

Using O80 despite a documented complication. Any antepartum, delivery, or postpartum complication — including lacerations and instrument-assisted delivery — disqualifies O80, which also permits only Z37.0 as its outcome code.

Assigning trimester by when the condition began rather than the encounter date. Trimester characters reflect the trimester at the encounter (or admission, for conditions developing during an inpatient stay).

Adding Z3A codes to abortive-outcome or postpartum encounters. Weeks of gestation codes accompany Chapter 15 codes only while the pregnancy is ongoing.

Reporting Z37 on more than the delivery encounter. The outcome-of-delivery code appears once, on the maternal delivery record, and never on postpartum visits.

Forgetting the fetus 7th character in multiple gestations. Categories like O31, O32, O35, O36, O41, O64, and O69 require a 7th character identifying the affected fetus — 0 for singletons, 1–9 for specific fetuses.

Coding gestational diabetes with a Chapter 4 diabetes code. Only pre-existing diabetes (O24.0-/O24.1-) takes an additional Chapter 4 code; gestational diabetes (O24.4-) stands alone, with insulin control taking precedence over diet when both are documented.

Final Exam Strategy for This Section

Chapter 15 rewards a checklist mentality. For every pregnancy question, run the same five checks: Is this the mother’s chart or the baby’s? Does an O code lead, or is the pregnancy documented as incidental? What trimester — and does Z3A apply? Is O80 truly clean, and does the Z37 outcome match? Does any category in play need a fetus 7th character? Write those five questions into your review materials next to the CPC Exam Cheat Sheet tables, and drill the O80 disqualifiers and Z37/Z38 jurisdiction until they are reflexes using the system in the CPC Exam Study Guide. Pregnancy questions are rule-dense but shallow — once the checklist is automatic, they become some of the most reliable points on the exam, especially when paired with the CPT side in Global OB Package & Maternity CPT Coding.

Frequently Asked Questions

The ICD-10-CM Official Guidelines for Coding and Reporting are the rulebook that governs how every diagnosis code is selected, sequenced, and reported. These guidelines are not optional recommendations — they are mandatory standards that all coders must follow. The CPC exam tests these guidelines extensively, and candidates who have not studied them thoroughly will miss questions they could otherwise answer. If you are just getting started with ICD-10-CM, review What Is ICD-10-CM and How ICD-10-CM Codes Are Built before diving into the guidelines.

This guide covers the most heavily tested guideline rules organized by topic, with real examples showing how each rule applies on the exam.

Structure of the ICD-10-CM Guidelines

The Official Guidelines are published annually by CMS and NCHS and are organized into four sections:

For the CPC exam, Section I and Section IV are the most critical because CPCs primarily work in outpatient settings. However, you need to understand Sections II and III well enough to distinguish inpatient rules from outpatient rules — the exam tests this distinction regularly. For a detailed comparison, see Outpatient vs Inpatient Coding Guidelines.

Key Conventions

Conventions are the instructions built into the code set itself — the symbols, abbreviations, and formatting rules that tell you how to interpret and apply codes. These are found in Section I.A of the guidelines.

Code to the Highest Level of Specificity

This is the most fundamental coding convention: always assign a code to the highest number of characters available. If a code has a 4th, 5th, 6th, or 7th character, you must include every applicable character. A code is only valid at the level where no further specificity exists.

Example: Coding type 2 diabetes mellitus with diabetic chronic kidney disease as E11.22 is correct. Coding it as E11 alone is invalid because further characters are required and available. See Diabetes Coding in ICD-10-CM for more on diabetes-specific rules.

The Placeholder Character “X”

ICD-10-CM uses “X” as a placeholder in two situations. First, certain codes have an “X” embedded within the code to maintain the required character length. Second, and more commonly tested, some codes require a 7th character extension but have fewer than six characters before it — the placeholder “X” fills positions 5 and/or 6 so the 7th character falls in the correct position.

Example: The initial encounter code for a toxic effect of unspecified pesticide, accidental, is T60.91XA. The “X” fills the 6th position so that “A” (initial encounter) falls in the 7th position. Omitting the “X” and coding T60.91A would be invalid.

7th Character Extensions

Many ICD-10-CM codes, particularly in Chapters 19 (Injury) and 20 (External Causes), require a 7th character that indicates the encounter type. The three most common 7th characters are:

• A — Initial encounter: the active treatment phase, regardless of which provider sees the patient
• D — Subsequent encounter: routine care during the healing phase
• S — Sequela: complications or conditions arising as a direct result of the original condition

A common exam mistake is assuming “initial encounter” means the patient’s first visit to that specific provider. It does not — “initial” means the patient is receiving active treatment for the condition. A patient can have an initial encounter (A) at a second or third provider if active treatment is still ongoing. For a complete breakdown of 7th character rules, see Injury Coding and 7th Characters.

Excludes Notes

Excludes notes are among the most heavily tested guideline conventions on the CPC exam. There are two types, and they mean very different things. For a full guide with examples, see Excludes1 vs Excludes2 Notes.

Excludes1 — “NOT Coded Here”

An Excludes1 note means the two conditions cannot occur together. The excluded code should never be used at the same time as the code above the Excludes1 note. If the patient has the excluded condition, you code the excluded condition instead of the code where the Excludes1 note appears.

Example: Under category F10 (Alcohol related disorders), there is an Excludes1 note for F10.21 (alcohol dependence, in remission). You cannot code both active alcohol dependence and alcohol dependence in remission simultaneously — the patient is either one or the other.

Excludes2 — “Not Included Here”

An Excludes2 note means the excluded condition is not part of the code above it, but the patient can have both conditions simultaneously. If the patient has both conditions, you assign codes for each.

Example: Under J44 (Other chronic obstructive pulmonary disease), there is an Excludes2 note for asthma (J45.-). A patient can have both COPD and asthma, and both should be coded when documented.

Sequencing Instructions: Code First, Use Additional Code, Code Also

These instructions tell you the required order when reporting multiple codes together. Understanding these is essential for correct ICD-10-CM sequencing.

Code First / Use Additional Code

These instructions appear in pairs. “Code first” under a code tells you that another code should be sequenced before this one. “Use additional code” under a different code tells you to add a secondary code after it. They work together to enforce sequencing.

Example: Under E08 (Diabetes mellitus due to underlying condition), you see “Code first the underlying condition.” If a patient has hemochromatosis (E83.11-) causing diabetes, you code E83.11- first, then E08.-.

Code Also

“Code also” means you should assign an additional code when appropriate, but unlike “Code first” / “Use additional code,” there is no required sequencing. Either code may be listed first depending on the circumstances and the reason for the encounter.

And / With

“And” in ICD-10-CM should be interpreted as “and/or” — it means the code applies when either or both conditions are present. “With” means the two conditions have an assumed causal relationship when documented in the same patient — you do not need the physician to explicitly state causality. This “with” convention is particularly important in diabetes coding and hypertension coding.

Outpatient Coding Guidelines (Section IV)

Section IV contains the rules specific to outpatient encounters — the setting most relevant to CPC coders. The most critical outpatient rules are:

Uncertain Diagnoses Are Never Coded

In the outpatient setting, do not code diagnoses documented as “probable,” “suspected,” “questionable,” “rule out,” or “working diagnosis.” Instead, code the signs and symptoms that are known and documented. This is the opposite of the inpatient rule and is tested on virtually every CPC exam.

First-Listed Diagnosis Selection

The first-listed diagnosis is the condition chiefly responsible for the services provided. This differs from the inpatient principal diagnosis, which is determined after study. In outpatient coding, the reason for the encounter drives the first-listed diagnosis.

For encounters where a patient presents for a test ordered by another provider, and no signs, symptoms, or diagnosis is known at the time, code the reason for the test if known, or Z01.89 (Encounter for other specified special examinations) if not.

Chronic Conditions

Chronic conditions managed or monitored during the visit should be coded. Code all conditions that coexist and affect patient care or management. Do not code chronic conditions that are documented but not addressed during the visit.

Encounters for Circumstances Other Than Disease or Injury

When a patient presents for a service other than treating an active disease — such as a screening, a vaccination, or aftercare — a Z-code is typically the first-listed diagnosis.

Commonly Tested Chapter-Specific Guidelines

Certain chapters of ICD-10-CM have their own guideline rules that override or supplement the general conventions. These are tested heavily on the CPC exam.

Chapter 4: Endocrine — Diabetes Mellitus (E08–E13)

Diabetes requires as many codes as necessary to describe all associated conditions. The “with” convention applies — if a diabetic patient has a condition listed under the diabetes code’s “with” subterms, the causal link is assumed. You do not need the physician to state “due to diabetes.” Type 2 is the default when the type is not documented. See the full guide at Diabetes Coding in ICD-10-CM.

Chapter 9: Circulatory — Hypertension

Hypertension with heart disease has an assumed causal relationship under the “with” convention — code I11 (Hypertensive heart disease) rather than coding hypertension and heart disease separately. Similarly, hypertension with chronic kidney disease uses category I12 or I13. Full details in Hypertension Coding in ICD-10-CM.

Chapter 2: Neoplasms (C00–D49)

Neoplasm coding requires determining whether the neoplasm is malignant (primary or secondary), benign, uncertain behavior, or unspecified. The Table of Neoplasms in the Alphabetic Index is the primary lookup tool. When a patient is admitted for treatment of a malignancy, the malignancy is the principal/first-listed diagnosis. See Neoplasm Coding in ICD-10-CM.

Chapter 1: Infectious Diseases — Sepsis

Sepsis coding follows strict sequencing rules. Sepsis (A41.-) is coded first, with R65.20 or R65.21 as an additional code for severe sepsis. If sepsis leads to organ dysfunction, the organ dysfunction code follows. The sequencing is mandatory regardless of the encounter setting. Full breakdown at Sepsis Coding Guidelines.

Chapter 19: Injury and External Causes

Injury codes require 7th character extensions (A, D, S). External cause codes (categories V00–Y99) are required as additional codes to identify how the injury occurred. For multiple injuries, sequence the most severe injury first unless the guidelines or circumstances dictate otherwise.

How to Study the Guidelines for the CPC Exam

The guidelines document is over 100 pages, but you do not need to memorize every line. Focus your study on:

1. Section IV (Outpatient) — Know every rule in this section. It directly governs the coding scenarios on the CPC exam.
2. The uncertain diagnosis rule — Understand the outpatient vs inpatient difference cold. This is tested every exam.
3. Excludes1 vs Excludes2 — Know the difference and be able to apply it.
4. Sequencing instructions — Code First, Use Additional Code, Code Also.
5. Chapter-specific rules for diabetes, hypertension, neoplasms, sepsis, and injuries — these chapters generate the most exam questions.
6. The “with” convention — Especially for diabetes and hypertension.

Tab your ICD-10-CM manual at the guideline sections you reference most often. Write quick notes in the margins next to the most tested rules. For a printable summary, see the CPC Exam Cheat Sheet, and for full exam preparation strategy, see the CPC Exam Study Guide.

Frequently Asked Questions

Signs and symptoms codes — found primarily in Chapter 18 (R00–R99) of ICD-10-CM — are among the most frequently used codes in outpatient settings and among the most frequently tested topics on the CPC exam. These codes describe clinical findings that have not yet been attributed to a definitive diagnosis: abnormal lab results, pain in various locations, fever, nausea, shortness of breath, and hundreds of other clinical presentations.

The coding guidelines have specific rules about when signs and symptoms should be coded, when they should not be coded, and how they interact with definitive diagnoses. Getting these rules wrong leads to overcoding (reporting symptoms alongside the diagnosis that explains them) or undercoding (failing to report symptoms when no definitive diagnosis has been established). Both errors appear as answer choices on the CPC exam.

This guide covers the complete set of rules for signs and symptoms coding, including the critical connection to the outpatient uncertain diagnosis rule and the relationship between symptoms and definitive diagnoses. For a broader overview of the coding framework, start with the ICD-10-CM coding guidelines.

What Are Signs and Symptoms Codes?

Signs and symptoms are clinical findings that the physician documents but that have not been linked to a specific underlying diagnosis. ICD-10-CM distinguishes between:

• Signs — Objective findings observed or measured by the clinician (elevated blood pressure reading, palpable mass, abnormal lab value, audible heart murmur)
• Symptoms — Subjective complaints reported by the patient (headache, chest pain, fatigue, dizziness, nausea)

Both are coded from Chapter 18 (Symptoms, Signs, and Abnormal Clinical and Laboratory Findings, Not Elsewhere Classified), which spans categories R00 through R99. However, some signs and symptoms are classified in body-system-specific chapters rather than Chapter 18 — for example, pain codes may appear in the musculoskeletal chapter for joint pain.

The Core Rule: When to Code Signs and Symptoms

The fundamental rule has two parts:

Code signs and symptoms when no definitive diagnosis has been established. If the physician documents symptoms but has not identified or confirmed the underlying cause, report the signs and symptoms codes. This is the standard approach in outpatient settings where the encounter may end before a definitive diagnosis is reached.

Do not code signs and symptoms when they are integral to a confirmed definitive diagnosis. If the physician has identified the underlying condition that explains the symptom, and the symptom is a routine part of that condition, you code only the definitive diagnosis. The symptom is considered “integral” — it is inherently part of the disease process and does not provide additional useful information.

Integral vs Non-Integral Symptoms

This distinction is where most coding errors occur.

Integral symptoms are signs and symptoms that are routinely associated with a disease and are expected to be present. They do not provide additional clinical information beyond what the definitive diagnosis already communicates.

Example: A patient diagnosed with pneumonia who has a cough and fever. Cough and fever are integral to pneumonia — you code only the pneumonia. Adding separate codes for cough (R05.-) and fever (R50.9) would be overcoding.

Non-integral symptoms are signs and symptoms that are not routinely associated with the diagnosed condition, or that represent a separate clinical concern.

Example: A patient diagnosed with type 2 diabetes who also has unexplained weight loss. While weight loss can occur with diabetes, it is not a routine finding that is always present. If the physician documents the weight loss as a separate concern requiring evaluation, it may be coded additionally.

The ICD-10-CM guidelines do not provide a definitive list of which symptoms are integral to which diagnoses. This requires clinical knowledge and judgment. However, the CPC exam typically makes the distinction clear in the scenario — if the symptom is obviously explained by the confirmed diagnosis, do not code it separately.

The Outpatient Uncertain Diagnosis Connection

Signs and symptoms coding is directly linked to the outpatient uncertain diagnosis rule from Section IV of the guidelines. This connection is tested on virtually every CPC exam.

The rule: In outpatient settings, you never code diagnoses documented as “probable,” “suspected,” “questionable,” “rule out,” “compatible with,” “consistent with,” or “working diagnosis.” Instead, you code the signs and symptoms to the highest degree of certainty.

How it works in practice:

A patient presents to the physician’s office with right upper quadrant abdominal pain. The physician examines the patient, orders an ultrasound, and documents “suspected cholecystitis — awaiting imaging results.”

• Correct outpatient coding: R10.11 (Right upper quadrant pain) — the confirmed symptom
• Incorrect outpatient coding: K81.9 (Cholecystitis, unspecified) — the suspected diagnosis that has not been confirmed

This rule means that signs and symptoms codes are the primary diagnostic codes in many outpatient encounters, particularly initial visits, emergency department encounters, and any encounter where testing is ordered but results are not yet available.

For the detailed comparison of how this rule differs in inpatient settings, see Outpatient vs Inpatient Coding Guidelines.

When Signs and Symptoms Codes ARE Reported with a Definitive Diagnosis

There are situations where you report both a definitive diagnosis and a signs/symptoms code. These exceptions are important for the CPC exam.

When the Symptom Is Not Explained by the Diagnosis

If a patient has a confirmed diagnosis plus a symptom that the diagnosis does not explain, code both. The symptom represents a separate clinical concern that the definitive diagnosis does not account for.

Example: A patient diagnosed with urinary tract infection (N39.0) who also has unexplained chest pain (R07.9). The chest pain is not a symptom of UTI, so it is coded separately if it is evaluated or managed during the encounter.

When a Code First / Use Additional Code Instruction Requires It

Some definitive diagnosis codes have “Use additional code” instructions directing you to add a signs/symptoms code. In these cases, the symptom code is mandatory as a secondary code.

Example: Certain neurological condition codes instruct “Use additional code to identify the type of seizure or convulsion.” Here, the symptom code (the seizure type) is added as a secondary code per the Tabular List instruction, even though a definitive diagnosis is established.

When the Symptom Provides Additional Important Clinical Information

If a symptom is clinically significant and not fully captured by the definitive diagnosis code, it may be reported additionally. This applies when the symptom affects patient management in a way not communicated by the diagnosis code alone.

Coding Abnormal Findings (R70–R94)

Categories R70 through R94 cover abnormal findings on laboratory tests, imaging studies, and function studies. These codes have specific usage rules:

Code abnormal findings when no definitive diagnosis has been established. If a lab test returns an abnormal result and the physician has not yet determined the cause, the abnormal finding code is appropriate.

Do not code abnormal findings when a definitive diagnosis has been established. If the abnormal lab result has been attributed to a specific condition, code the condition instead of the abnormal finding.

Example: A patient’s blood work shows elevated glucose (R73.09). If the physician has not diagnosed diabetes, R73.09 is the appropriate code. If the physician has confirmed type 2 diabetes, code E11.65 (Type 2 diabetes with hyperglycemia) or the appropriate diabetes code — not the abnormal glucose finding.

Do not code abnormal findings that are part of normal variation or that are not clinically significant. Not every out-of-range lab value warrants a code. The physician must document the abnormality as clinically significant or must order further workup based on it.

How the CPC Exam Tests Signs and Symptoms Coding

Pattern 1 — Symptom vs Definitive Diagnosis

The scenario presents a patient with documented symptoms and a confirmed diagnosis. One answer choice includes both the symptom and the diagnosis codes. Another includes only the diagnosis code. The correct answer is typically the diagnosis code alone — because the symptom is integral to the confirmed diagnosis.

Pattern 2 — Uncertain Diagnosis in Outpatient Setting

The scenario describes an outpatient encounter with a “suspected” or “rule out” diagnosis. One answer choice codes the uncertain diagnosis. Another codes the signs and symptoms. The correct answer is always the signs and symptoms in outpatient settings.

Pattern 3 — Multiple Symptoms, No Diagnosis

The scenario describes a patient presenting with multiple symptoms and no definitive diagnosis established during the encounter. The correct answer codes all relevant signs and symptoms that were evaluated. The first-listed diagnosis is the symptom chiefly responsible for the encounter.

Pattern 4 — Non-Integral Symptom

The scenario presents a confirmed diagnosis plus a symptom that is clearly unrelated to that diagnosis. The correct answer includes both codes — the definitive diagnosis and the non-integral symptom — because the symptom represents a separate clinical concern. This tests whether you know that symptoms are sometimes appropriately coded alongside a definitive diagnosis.

Common Signs and Symptoms Tested on the CPC Exam

Common Mistakes

Coding symptoms alongside the definitive diagnosis that explains them. If the physician confirms pneumonia, do not also code the cough and fever. The symptoms are integral.

Coding an uncertain diagnosis instead of symptoms in the outpatient setting. “Suspected cholecystitis” in an outpatient encounter means you code the abdominal pain, not cholecystitis.

Not coding symptoms when no definitive diagnosis exists. Some coders hesitate to use R-codes, but they are the correct choice when no definitive diagnosis has been established. Signs and symptoms codes are legitimate, billable codes — not placeholder codes.

Using unspecified symptom codes when more specific codes exist. Always code to the highest level of specificity. If the documentation specifies right upper quadrant abdominal pain, code R10.11 — not R10.9 (unspecified abdominal pain). See How ICD-10-CM Codes Are Built for specificity requirements.

Frequently Asked Questions

A combination code is a single ICD-10-CM code that captures two or more clinical concepts in one code. Instead of reporting multiple separate codes, a combination code lets you report a diagnosis along with its complication, manifestation, or associated sign or symptom using just one code. Combination codes are one of the defining features of ICD-10-CM and understanding them is essential for accurate coding and for the CPC exam.

The CPC exam tests combination codes in two ways: by presenting a scenario where the combination code is the correct answer instead of two separate codes, and by presenting a scenario where a combination code does not exist and you need to assign multiple codes. Knowing when a combination code exists — and when it does not — separates strong coders from average ones.

What Is a Combination Code?

The ICD-10-CM Official Guidelines define a combination code as “a single code used to classify two diagnoses, or a diagnosis with an associated secondary process (manifestation), or a diagnosis with an associated complication.” When a combination code exists and fully describes all elements of the documented condition, you assign only that single code. You do not assign separate codes for the individual components.

This rule is stated directly in the ICD-10-CM coding guidelines: “When a single code that includes all elements documented in the diagnosis is listed in the Tabular List, the combination code should be assigned.” An additional code should be assigned as a secondary code only when the combination code does not fully describe all the documented elements.

Key principle: Always look for a combination code first. Only use multiple codes when no single combination code captures the complete clinical picture.

The Three Types of Combination Codes

Combination codes in ICD-10-CM fall into three categories based on what clinical concepts they combine.

Type 1 — Two Diagnoses Combined

These codes capture two separate but related diagnoses in a single code. They exist because certain conditions occur together so frequently that ICD-10-CM provides a single code to describe both.

Examples:

In each case, you would not code the two conditions separately when this combination code exists. For instance, if a patient has type 2 diabetes with chronic kidney disease, you code E11.22 — you do not code type 2 diabetes (E11.9) and chronic kidney disease (N18.-) separately. See Diabetes Coding in ICD-10-CM for more on diabetes combination codes.

Type 2 — Diagnosis with Associated Complication or Manifestation

These codes capture an underlying condition and a complication or manifestation that results from it. Before ICD-10-CM, many of these required dual coding with etiology/manifestation pairs. Now many have dedicated combination codes.

Examples:

Notice how K80.12 actually combines three clinical concepts — gallstones, the type of cholecystitis (acute and chronic), and the presence of obstruction — all in one code. This is one of the most complex combination codes and demonstrates the specificity ICD-10-CM was designed to achieve.

Type 3 — Diagnosis with Associated Sign or Symptom

These codes capture a confirmed diagnosis together with a specific sign or symptom. Under normal ICD-10-CM rules, you do not code signs and symptoms when a definitive diagnosis is established. However, when a combination code exists that includes both, it is appropriate and required to use it.

Examples:

How to Identify a Combination Code in Practice

The process for finding combination codes involves both the Alphabetic Index and the Tabular List.

Step 1 — Start in the Alphabetic Index

Look up the primary condition. Under the main term, look for subterms that describe the associated condition, complication, or symptom. The Alphabetic Index is organized hierarchically — subterms under the main entry indicate combination code availability.

For example, looking up “Diabetes” in the Index reveals subterms like “with” followed by extensive indented entries for complications: amyotrophy, arthropathy, cataract, chronic kidney disease, dermatitis, foot ulcer, gangrene, and many more. Each of these points to a combination code.

Step 2 — Verify in the Tabular List

Never code from the Alphabetic Index alone. Locate the code in the Tabular List to confirm it is valid and to check for additional characters, instructional notes, and Excludes notes. The Tabular List may reveal that additional characters are needed for laterality, episode of care, or other specificity.

Step 3 — Check the “With” Convention

ICD-10-CM’s “with” convention is particularly important for combination codes. When a combination code exists for a condition “with” a complication, the causal link is assumed — you do not need the physician to explicitly state that the complication is caused by the primary condition. This convention applies to diabetes and hypertension coding among others.

For example, if a patient has type 2 diabetes and peripheral neuropathy, and both are documented, you code E11.42 (Type 2 diabetes mellitus with diabetic polyneuropathy). You do not need the physician to write “peripheral neuropathy due to diabetes” — the “with” convention assumes the relationship.

Step 4 — Determine If the Combination Code Is Complete

After identifying a potential combination code, ask: does this single code describe everything documented? If the answer is yes, assign only the combination code. If the answer is no — for example, the patient has additional complications not captured by the combination code — assign the combination code plus additional codes for the elements not covered.

When Combination Codes Do NOT Exist

Not every pair of related conditions has a combination code. When no combination code exists, you must assign separate codes, typically following sequencing rules like “Code first” and “Use additional code.”

Common scenarios without combination codes:

• A condition with a manifestation where only etiology/manifestation coding is available (the Tabular List will show “Code first” / “Use additional code” instructions)
• Two unrelated conditions that happen to be documented together
• A condition with a complication not listed in the combination code’s subcategories

The exam tests this by presenting a scenario where a candidate might assume a combination code exists when it does not. If the Tabular List does not include a subcategory for the specific complication documented, you cannot use a combination code — you must assign separate codes.

How the CPC Exam Tests Combination Codes

Pattern 1: Combination Code vs Two Separate Codes

The most common pattern presents a scenario and offers answer choices that include both the combination code and two separate codes. The correct answer is the combination code.

Example question pattern: A patient presents with type 2 diabetes and diabetic retinopathy. The answer choices include E11.319 (the combination code for type 2 diabetes with unspecified diabetic retinopathy) and a pair of codes (E11.9 + H35.00). The correct answer is the single combination code.

Pattern 2: No Combination Code Available

The question presents two related conditions where no combination code exists, and the answer choices include a fabricated combination code alongside the correct dual-coding answer. You need to recognize that the combination code does not exist.

Pattern 3: Incomplete Combination Code

The scenario documents more clinical detail than a single combination code captures. The correct answer includes the combination code plus an additional code for the element not covered.

Pattern 4: The “With” Convention Application

The question presents two conditions (such as diabetes and a complication) without the physician explicitly stating a causal link. One answer choice uses the combination code (correct), and another uses separate codes. This tests whether you know the “with” convention assumes the relationship.

Common Mistakes with Combination Codes

Coding two separate codes when a combination code exists. Always check for a combination code before assigning multiple codes. If the combination code fully describes the documented conditions, use it alone.

Using a combination code when the clinical detail does not match. A combination code for “with obstruction” should not be used if the documentation does not mention obstruction. Read the full code description.

Missing the “with” convention. New coders sometimes look for explicit documentation of causality (“due to,” “caused by”) when the “with” convention does not require it. For categories that use the “with” convention, the association is assumed.

Ignoring additional specificity. Some combination codes have additional characters for laterality, encounter type, or severity. Always code to the highest level of specificity as required by the ICD-10-CM code structure.

Frequently Asked Questions

Diabetes mellitus is one of the most frequently coded conditions in medical coding — and one of the most heavily tested topics on the CPC exam. ICD-10-CM uses a combination code system for diabetes that captures both the type of diabetes and any associated complications in a single code. A coder who understands this system can handle diabetes charts quickly and confidently; a coder who doesn’t will miscombine types and complications, miss sequencing instructions, or forget the insulin-use code that must accompany certain Type 2 diagnoses.

This guide walks through the full ICD-10-CM diabetes coding framework: the code categories, how combination codes work, complication coding rules, secondary diabetes, pregnancy-related diabetes, and every sequencing rule tested on the CPC exam.

The ICD-10-CM Diabetes Code Categories

ICD-10-CM organizes diabetes mellitus under categories E08–E13 in Chapter 4 (Endocrine, Nutritional and Metabolic Diseases). Each category corresponds to a specific etiology or type:

There is no E12 in ICD-10-CM — that number is unassigned. The gap trips up candidates who try to memorize sequential code numbers rather than learning what each category means.

📌 CPC Exam Tip: The most-tested distinction is E10 vs. E11. Type 1 is autoimmune, typically early-onset, and inherently insulin-dependent. Type 2 is the default when documentation doesn’t specify type. Many CPC exam questions include the phrase “insulin-dependent” to see if candidates correctly recognize that a Type 2 patient on insulin is still coded E11, not E10. The need for insulin does not change the diabetes type — it requires an additional code (Z79.4).

How Combination Codes Work for Diabetes

ICD-10-CM uses combination codes for diabetes — codes that capture both the underlying disease and the complication in a single code. The structure is: [Category].[Complication subcode]

Examples:

• E11.40 — Type 2 diabetes mellitus with diabetic neuropathy, unspecified
• E10.311 — Type 1 diabetes mellitus with unspecified diabetic retinopathy with macular edema
• E11.65 — Type 2 diabetes mellitus with hyperglycemia

The combination code structure is one of ICD-10-CM‘s major improvements over ICD-9-CM, where diabetes and its complications required two separate codes. In ICD-10-CM, a single code documents both — unless multiple distinct complications are present, in which case each complication gets its own combination code within the same category.

📌 CPC Exam Tip: CPC exam questions frequently give a diagnosis like “Type 2 diabetes with diabetic peripheral neuropathy” and ask for the code. The answer is a single combination code from E11 (e.g., E11.40), not two separate codes. Selecting two codes where one combination code exists is a common exam error.

The Default Rule: Type 2 When Type Is Not Specified

The ICD-10-CM Official Guidelines for Coding and Reporting include a critical default rule:

When the medical record does not specify the type of diabetes, code Type 2 (E11).

If a physician documents “diabetes mellitus” without indicating Type 1, Type 2, gestational, or a specific etiology, the coder assigns E11 by convention. This reflects the real-world prevalence of Type 2 — approximately 90–95% of all diabetes cases.

The coder may NOT make assumptions about the type based on the patient’s age, insulin use, or other clinical factors. If it isn’t documented, the answer is E11.

Complication Subcodes: What Each Range Covers

Each diabetes category (E10, E11, E08, E09, E13) uses the same complication subcode structure. The subcodes are organized by body system:

Diabetic Kidney Disease (E_x_.2x)

When diabetic CKD is coded, an additional N18.- code is required to identify the specific CKD stage — the ICD-10-CM “use additional code” instruction at E11.22 mandates this.

Diabetic Eye Disease (E_x_.3xx)

Retinopathy codes require specifying whether macular edema is present — this is the critical distinction within the E11.3xx range. Proliferative vs. non-proliferative retinopathy adds further granularity at the 5th and 6th character level.

Diabetic Neurological Complications (E_x_.4x)

Polyneuropathy (E11.42, affecting multiple nerves) is the most common neuropathic pattern and the most frequently coded. Mononeuropathy (E11.41) affects a single nerve and is coded when specifically documented.

Diabetic Circulatory Complications (E_x_.5x)

When gangrene is present with diabetic peripheral angiopathy, E11.52 is used — the combination code captures both. Do not separately code the gangrene.

Skin, Foot, and Other Complications (E_x_.6x)

For diabetic foot ulcers (E11.621), an additional code from L97.- is required to identify the ulcer site and severity — another “use additional code” instruction in the ICD-10-CM tabular.

Insulin Use: Z79.4 and Z79.84

When a patient with Type 2 diabetes is being treated with insulin, an additional code is required:

Z79.4 — Long-term (current) use of insulin

This code is never used for Type 1 diabetes — E10 already implies insulin dependence. Z79.4 applies exclusively to Type 2 (E11) and other non-Type-1 categories (E08, E09, E13) when insulin is prescribed as part of management.

When a Type 2 patient is treated with oral hypoglycemic agents (such as metformin), the additional code is:

Z79.84 — Long-term (current) use of oral hypoglycemic drugs

📌 CPC Exam Tip: One of the most reliably tested diabetes coding nuances: “Type 2 diabetes patient who takes insulin daily” requires both the E11 combination code AND Z79.4. Missing Z79.4 is an incomplete code selection. Always ask — if the patient has Type 2 diabetes, is insulin use documented? If yes, Z79.4 is required.

Secondary Diabetes: E08 and E09

Secondary diabetes — diabetes caused by another disease or substance rather than the patient’s own autoimmune or genetic factors — uses E08 or E09 depending on the cause.

E08: Diabetes mellitus due to underlying condition. When another disease process causes or contributes to diabetes development (such as chronic pancreatitis, cystic fibrosis, Cushing syndrome, or acromegaly), E08 is the category. Per the etiology/manifestation convention in ICD-10-CM, the underlying causal condition is sequenced first — E08 follows it.

E09: Drug or chemical induced diabetes mellitus. When a medication or toxic substance caused the diabetes, E09 is used. An additional code from the Table of Drugs and Chemicals (T36–T65) identifies the substance and whether the circumstance is adverse effect, underdosing, or poisoning. For adverse effects (correct drug, correct dose, properly administered), E09 is sequenced first; for poisoning, the poisoning code leads.

E13 covers all other secondary diabetes not captured by E08 or E09 — most commonly post-pancreatectomy diabetes or diabetes following other pancreatic surgery.

Gestational and Pregnancy-Related Diabetes

Diabetes in pregnancy uses the O24 category — not E10 or E11. The O24 codes apply to gestational diabetes (diabetes that develops during pregnancy in a woman who did not have pre-existing diabetes) and are used during pregnancy encounters.

For a woman with pre-existing Type 1 or Type 2 diabetes who becomes pregnant, the appropriate E10 or E11 code is used along with O24.0x (pre-existing Type 1 in pregnancy) or O24.1x (pre-existing Type 2 in pregnancy) to capture the pregnancy context.

📌 CPC Exam Tip: Do not use E11 for gestational diabetes. The CPC exam tests this by presenting a pregnant patient with elevated glucose and asking for the correct code. If diabetes arose during pregnancy and was not pre-existing, the answer is always in the O24 category — never E11.9 or E11.649.

Sequencing Rules for Multiple Diabetic Complications

When a patient has more than one diabetic complication, each complication is coded separately using its own combination code within the same diabetes category. No single code captures two different complications simultaneously.

Example: A Type 2 diabetes patient with documented polyneuropathy and diabetic chronic kidney disease, stage 3, on insulin:

• E11.42 — Type 2 DM with diabetic polyneuropathy
• E11.22 — Type 2 DM with diabetic chronic kidney disease, stage 1–2 (or the appropriate stage code)
• N18.3 — Chronic kidney disease, stage 3 (required by “use additional code” instruction)
• Z79.4 — Long-term use of insulin

In outpatient settings, the condition chiefly responsible for the visit is sequenced first. In inpatient settings, the principal diagnosis per UHDDS criteria leads the claim.

Clinical Examples

Example 1: Documentation: “Type 2 diabetes mellitus with diabetic foot ulcer, left heel; patient on insulin.”

• E11.621: Type 2 DM with foot ulcer
• L97.429: Non-pressure chronic ulcer of left heel and midfoot, unspecified severity
• Z79.4: Long-term use of insulin

Example 2: Documentation: “Chronic pancreatitis with secondary diabetes mellitus, no complications, diet-controlled.”

• K86.1: Chronic pancreatitis (sequenced first — etiology/manifestation)
• E08.9: Diabetes due to underlying condition, without complications

Example 3: Documentation: “Insulin-dependent diabetes — Type 2. No current complications.”

• E11.9: Type 2 DM without complications
• Z79.4: Long-term use of insulin

(The phrase “insulin-dependent” does not change the type. Type 2 is coded because it is explicitly documented.)

Frequently Asked Questions

Excludes notes are instructional notes in the ICD-10-CM Tabular List that tell coders when two codes can or cannot be used together. There are two types — Excludes1 and Excludes2 — and they mean very different things. Confusing them is one of the most common coding errors, and the CPC exam tests the distinction directly. If you can reliably tell the difference between Excludes1 and Excludes2 and apply each rule correctly, you will answer these questions faster and with more confidence than most candidates.

This guide covers both types of Excludes notes with real ICD-10-CM examples, walks through the important exception to the Excludes1 rule, and explains how the CPC exam tests these concepts. For the broader context of ICD-10-CM coding rules, see the ICD-10-CM Official Coding Guidelines.

Why Do Exclusion Notes Exist?

The ICD-10-CM code set contains over 72,000 codes. Many conditions overlap, share symptoms, or exist in related categories. Without exclusion notes, coders would have no guidance on which codes can or cannot coexist on the same claim. The result would be contradictory claims (coding both active disease and disease in remission), redundant claims (coding a condition twice in different categories), and inaccurate clinical pictures.

Excludes notes provide the rules that prevent these problems. They are printed directly in the Tabular List under the relevant code or category, and they are binding — ignoring them is a coding error.

Excludes1 — “NOT Coded Here” (Mutually Exclusive)

An Excludes1 note means the code above it and the excluded code are mutually exclusive — they cannot occur together in the same patient at the same time. The Excludes1 note says: “this condition and the excluded condition cannot reasonably exist simultaneously.”

What the Excludes1 Note Looks Like

In the Tabular List, an Excludes1 note appears under a code or category header with the label “Excludes1:” followed by a list of excluded codes or categories.

Real Examples of Excludes1

Example 1: Diabetes in remission vs active diabetes

Under category E08–E13 (Diabetes mellitus), the code for diabetes “in remission” (such as E11.65 — Type 2 diabetes with hyperglycemia) has an Excludes1 relationship with certain other diabetes codes. A patient cannot have active diabetes with hyperglycemia and diabetes in remission simultaneously — the conditions are mutually exclusive.

Example 2: Acute vs chronic conditions

Under J20 (Acute bronchitis), there is an Excludes1 note for J41 (Simple chronic bronchitis). A patient cannot have both acute bronchitis and simple chronic bronchitis coded at the same time in certain contexts — the Excludes1 note indicates these are mutually exclusive classifications.

Example 3: Congenital vs acquired

Under Q65 (Congenital deformities of hip), there is an Excludes1 note for M16 (Osteoarthritis of hip). A congenital hip deformity code and an acquired osteoarthritis code in the same category cannot both be assigned for the same hip condition — the etiology is either congenital or acquired, not both.

The Rule in Practice

When you encounter an Excludes1 note, you have two options:

1. Code the condition that is actually present. If the patient has the excluded condition rather than the condition listed in the category, code the excluded condition instead.
2. Never code both simultaneously. Assigning both codes on the same encounter is a coding error.

Excludes2 — “Not Included Here” (Can Coexist)

An Excludes2 note means the excluded condition is not part of the code or category where the note appears, but the patient can have both conditions at the same time. Both codes can be assigned if both conditions are documented.

What the Excludes2 Note Looks Like

The format is the same as Excludes1 — it appears under a code or category with “Excludes2:” followed by excluded codes. The critical difference is in meaning, not formatting.

Real Examples of Excludes2

Example 1: COPD and asthma

Under J44 (Other chronic obstructive pulmonary disease), there is an Excludes2 note for J45 (Asthma). This means COPD (J44) does not include asthma — they are separate conditions, a patient can have both COPD and asthma, and if the patient has both documented, code both J44.- and J45.-

Example 2: Osteoporosis and pathological fracture

Under M80 (Osteoporosis with current pathological fracture), there is an Excludes2 note for M81 (Osteoporosis without current pathological fracture). These are not the same code — one includes a fracture and the other does not — but a patient could have osteoporosis with a pathological fracture at one site (coded with M80) and osteoporosis without fracture documented at another context.

Example 3: Anxiety and depression

Under F41 (Other anxiety disorders), there is an Excludes2 note for F32 (Depressive episode) and F33 (Recurrent depressive disorder). A patient can have both an anxiety disorder and depression — they commonly coexist. Code both when both are documented and managed.

The Rule in Practice

When you encounter an Excludes2 note: The excluded condition is not part of the current code. The code you are looking at does not include the excluded condition within its definition. If the patient has both, code both. Assign separate codes for each documented condition. The Excludes2 note is informational. It tells you where to find the code for the excluded condition — it does not prohibit coding both.

Side-by-Side Comparison

The memory aid in the last row is a popular trick: Excludes1 = pick one. Excludes2 = you can use two.

The Exception to the Excludes1 Rule

There is one important exception to the Excludes1 rule that the CPC exam has tested. The ICD-10-CM guidelines state that when two conditions classified as mutually exclusive by an Excludes1 note are both documented by the physician and confirmed to coexist, both codes may be assigned. This exception is rare and should only be applied when the physician explicitly documents that the patient has both conditions simultaneously.

Example: If a physician documents that a patient has both type 1 and type 2 diabetes (an extremely rare but documented clinical scenario), the coder would assign both codes despite the Excludes1 note, because the physician has confirmed both conditions exist. In practice, this exception is almost never applied — but knowing it exists prevents you from eliminating a correct answer on the CPC exam solely because of an Excludes1 note.

Important: This exception does not mean you can ignore Excludes1 notes routinely. It means that physician documentation overrides the note in rare cases where both conditions are explicitly confirmed.

Excludes Notes Appear at Different Hierarchy Levels

An important detail that trips up new coders is that Excludes notes can appear at several different levels of the ICD-10-CM hierarchy — the chapter level, the block or section level, the category level, or the individual code level — and a note’s placement determines how broadly it applies. A chapter-level Excludes note applies to every code within that entire chapter, a block-level note applies to a range of related categories, a category-level note applies to every code within that three-character category, and a code-level note applies only to that specific code. When researching whether two conditions can be coded together, check for Excludes notes at every level above the specific code you are considering, not just at the code itself, since a broader note higher in the hierarchy still governs even if no note appears at the specific code level.

Applying Both Note Types in the Same Category

Categories frequently contain both Excludes1 and Excludes2 notes simultaneously, each referring to different excluded conditions, and coders must evaluate each note independently rather than assuming a category is governed by only one exclusion type. For example, a single respiratory condition category might have an Excludes1 note ruling out one mutually exclusive condition while also carrying an Excludes2 note confirming that a different, commonly coexisting condition may be coded separately. Reading every instructional note listed under a category, rather than stopping after finding the first Excludes note, is necessary to catch all of the coding restrictions and allowances that apply.

Other Important Instructional Notes

While Excludes notes are the most frequently tested, the ICD-10-CM Tabular List contains other instructional notes you should know:

Includes Notes

An “Includes” note appears under a category to clarify what conditions are covered by that category. It lists additional terms or conditions considered part of the category even if not explicitly named in the code titles.

Inclusion Terms

Listed under specific codes, inclusion terms are diagnoses or synonyms that are classified to that code. If the physician documents a term listed as an inclusion term, you assign that code.

“Code First” and “Use Additional Code”

These sequencing instructions tell you the required order when two codes must be reported together. “Code first” means another code should precede the current code. “Use additional code” means an additional code should follow. See ICD-10-CM sequencing rules for full details.

“Code Also”

Unlike “Code first” / “Use additional code,” a “Code also” instruction does not specify sequencing. It simply tells you that an additional code may be needed — either code can be sequenced first depending on the circumstances.

How the CPC Exam Tests Excludes Notes

Pattern 1: “Can These Be Coded Together?”

The question presents two conditions and asks whether both codes can be assigned. If an Excludes1 note exists between them, the answer is no (with the rare exception). If an Excludes2 note exists, the answer is yes when both are documented.

Pattern 2: Selecting the Correct Code

The question presents a clinical scenario where the correct answer depends on understanding which code category to use. The wrong answer is a code from a category that has an Excludes1 note for the documented condition. The correct answer is the code from the category where the condition actually belongs.

Pattern 3: Multiple Code Assignment

The scenario documents two coexisting conditions that have an Excludes2 relationship. One answer choice includes both codes (correct); another includes only one code (incorrect, because the Excludes2 note confirms both can be assigned).

Pattern 4: The Exception Question

The scenario presents a rare situation where two Excludes1-related conditions are both documented as confirmed by the physician. The correct answer assigns both codes, testing whether you know the exception.

CPC Exam Tip: When you see an Excludes note question, your first job is to identify whether it is Excludes1 or Excludes2. Open your ICD-10-CM manual to the relevant code and read the note type. The answer follows directly from the note type in nearly every case.

For study preparation strategies, see the CPC Exam Study Guide and CPC Exam Cheat Sheet.

Frequently Asked Questions

Hypertension is one of the most commonly coded conditions in outpatient and inpatient settings. It is also one of the most error-prone areas in ICD-10-CM because coding hypertension is not just about finding the right blood pressure code — it requires understanding presumed causal relationships, combination code logic, and sequencing rules that trip up even experienced coders.

This guide walks through every hypertension category in ICD-10-CM, explains the unique “presumed causal” relationship rule, and provides clinical scenarios that mirror CPC exam questions.

The Four Hypertension Categories

ICD-10-CM organizes hypertension into four main categories. Each one covers a different combination of conditions. The category a patient falls into depends on what coexisting conditions are documented alongside the hypertension:

Understanding ICD-10 code structure helps you see how these categories branch. I10 is a standalone code (no additional characters needed). I11, I12, and I13 require additional characters to specify severity and whether heart failure is present.

I10 — Essential Hypertension

I10 is the simplest hypertension code. Use it when the patient has primary (essential) hypertension with no documented heart disease or chronic kidney disease. I10 covers high blood pressure, hypertension NOS, hypertensive vascular disease, and systemic arterial hypertension.

I10 does NOT require additional characters — it is a complete, billable code on its own.

What I10 Does Not Cover

I10 does not cover secondary hypertension (I15.-), hypertensive crisis (I16.-), pulmonary hypertension (I27.-), or hypertension complicating pregnancy (O10–O16). These are separate categories with their own coding rules. Secondary hypertension always requires two codes — one from I15 for the hypertension, and one for the underlying cause.

The Presumed Causal Relationship Rule

This is the single most important rule in hypertension coding — and one of the most frequently tested concepts on the CPC exam.

When a patient has both hypertension and heart disease, ICD-10-CM presumes the heart disease is caused by the hypertension. You do not need the provider to explicitly state “hypertensive heart disease” in the documentation. If the patient has hypertension and heart failure documented in the same record, assign a code from I11.- unless the provider specifically documents that the heart condition is NOT due to hypertension.

The same presumed-causal relationship applies to hypertension and chronic kidney disease. If a patient has both hypertension and CKD stages 1–5 or ESRD, assign a code from I12.- regardless of whether the provider states a causal link.

When the Relationship Is NOT Assumed

There are specific conditions where the causal link is NOT presumed, even when documented alongside hypertension:

Clinical Example: A patient record documents “hypertension, heart failure, and stroke.” For the hypertension and heart failure, the causal relationship IS presumed — code I11.0 (hypertensive heart disease with heart failure). For the stroke, the provider must explicitly document “stroke due to hypertension” or “hypertensive cerebrovascular disease” before you can code a causal relationship. Without that documentation, code the stroke and hypertension separately.

I11 — Hypertensive Heart Disease

Category I11 is used when a patient has hypertension with heart disease (heart failure, cardiomyopathy, or cardiomegaly). It has two subcategories:

The distinction between I11.0 and I11.9 hinges entirely on whether heart failure is present. If the patient has hypertension with cardiomegaly but no heart failure, use I11.9. If heart failure is documented, use I11.0 plus a code from I50.- to specify systolic, diastolic, or combined heart failure and whether it is acute, chronic, or acute on chronic.

Clinical Example: Patient documented with “hypertension and diastolic heart failure, chronic.” Correct coding: I11.0 (hypertensive heart disease with heart failure) + I50.32 (chronic diastolic heart failure).

I12 — Hypertensive Chronic Kidney Disease

Category I12 is used when a patient has both hypertension and CKD. The causal relationship is presumed — no explicit link is needed in the documentation. I12 has two subcategories based on CKD stage:

Always assign an additional code from N18.- to identify the stage of CKD. This is a mandatory “use additional code” instruction. Without the N18 code, the claim is incomplete and does not communicate CKD severity.

Clinical Example: Patient has hypertension and stage 3 CKD documented. Correct coding: I12.9 (hypertensive CKD, stage 1–4) + N18.3 (CKD stage 3, unspecified). There is no need for the provider to say “CKD due to hypertension” — the causal relationship is presumed.

I13 — Hypertensive Heart Disease and CKD

Category I13 is the most complex hypertension category. It applies when a patient has all three conditions: hypertension, heart disease, and CKD. The presumed causal relationship applies to both the heart disease and the CKD.

I13 codes require up to two additional codes — one from I50.- if heart failure is present, and one from N18.- for CKD stage. This means a single patient encounter may require three codes total to fully describe the hypertensive condition.

Clinical Example: Patient documented with hypertension, systolic heart failure (acute on chronic), and stage 4 CKD. Correct coding: I13.0 (hypertensive heart and CKD with heart failure, stage 1–4) + I50.23 (acute on chronic systolic heart failure) + N18.4 (CKD stage 4).

Hypertensive Crisis — I16

Hypertensive crisis is coded separately from chronic hypertension. Category I16 covers acute, dangerously elevated blood pressure:

I16.0 is hypertensive urgency — severely elevated blood pressure without acute organ damage. I16.1 is hypertensive emergency — severely elevated blood pressure WITH acute organ damage (encephalopathy, pulmonary edema, acute kidney injury, aortic dissection). I16.9 is hypertensive crisis, unspecified.

For all I16 codes, assign an additional code to identify the underlying chronic hypertension type (I10, I11, I12, or I13). This follows ICD-10 sequencing rules — the acute condition (I16) is listed first, followed by the chronic condition.

Step-by-Step Coding Decision Tree

Follow this sequence when coding hypertension:

Step 1 — Confirm the type of hypertension. Is it primary/essential or secondary? If secondary, use I15.- with a code for the underlying cause. If primary, continue.

Step 2 — Check for coexisting heart disease. Is heart failure, cardiomyopathy, or cardiomegaly documented? If no heart disease and no CKD → use I10. If heart disease present → continue to step 3.

Step 3 — Check for coexisting CKD. If heart disease present but no CKD → use I11 (with I50.- if heart failure). If CKD present but no heart disease → use I12 (with N18.-). If BOTH heart disease AND CKD → use I13 (with I50.- if heart failure AND N18.-).

Step 4 — Check for hypertensive crisis. If acute blood pressure crisis is documented → assign I16.0 or I16.1 first, then the appropriate chronic hypertension code.

Step 5 — Assign all required additional codes. For I50.- (heart failure type and acuity) and N18.- (CKD stage). Missing either additional code results in an incomplete claim.

Common CPC Exam Scenarios

Understanding how these rules apply to exam-style questions is critical. Here are patterns that appear frequently:

Scenario 1: Patient with hypertension and congestive heart failure. Answer: I11.0 + I50.9 (heart failure unspecified). The causal relationship is presumed — no documentation of “hypertensive heart failure” is needed.

Scenario 2: Patient with hypertension and stage 3 CKD and systolic heart failure. Answer: I13.0 + I50.20 + N18.3. All three conditions are present, so I13 is correct. Both I50 and N18 additional codes are required.

Scenario 3: Patient with hypertension and a stroke. Answer: I10 + the stroke code (I63.-). The causal relationship between hypertension and cerebrovascular disease is NOT presumed. Unless the provider documents “hypertensive cerebrovascular disease,” code them separately.

Scenario 4: Patient with hypertension and acute kidney injury. Answer: I10 + N17.- (AKI code). The presumed causal rule does NOT apply to AKI — only to CKD. Code separately.

Hypertension coding connects directly to other ICD-10 concepts. Understanding combination codes helps explain why I11, I12, and I13 exist — they capture multiple conditions in a single code. The diabetes coding guide covers similar presumed-causal logic for diabetic complications. And knowing when to assign a code for signs and symptoms versus an established diagnosis is important when blood pressure readings are elevated but no hypertension diagnosis has been confirmed.

Frequently Asked Questions